Here are some sites I use/have used to help me build my craft. Feel free to leave your own suggested sites in the comments.
Free Writing Resources
15 Minutes of delving into various topics related to genre fiction. Always ends with a writing prompt.
Hide and Create
30 Minute discussion of various aspects of genre fiction.
Grammar Girl's Quick and Dirty Tips
6 Minutes-ish addressing specific aspects of grammar, not genre focused.
Stuff You Should Know
45-60 Minutes of interesting bits of reality. Good for research and idea-sparking.
Write About Dragons
Brandon Sanderson's lectures on creative writing at BYU.
Geek and Sundry--The Storyboard [currently on hiatus]
Patrick Rothfuss hosts discussions about writing.
This is a show about game development, but many of their topics are equally applicable to creative endeavors of any kind.
Helps you proofread your own work
Pretty much everything you wanted to know about markets
A place to keep track of your submission history
David Farland's Daily Kick in the Pants
He kicks you in the pants. You're going to like it.
A great place to chat about fantasy
A great place to chat about writing fantasy
Even more research
Writers of the Future Forum
Full of dedicated aspiring writers
Neo-pro writers and beyond. (has qualification requirements, please check to make sure you're eligible before applying)